docs: CONTRIBUTING sign off

Signed-off-by: Jan Kowalleck <[email protected]>

Author: jkowalleck

CONTRIBUTING.md

@@ -5,9 +5,9 @@ But please read the
 [CycloneDX contributing guidelines](https://github.com/CycloneDX/.github/blob/master/CONTRIBUTING.md)
 first.
 
-## Sign your commits
+## Sign off your commits
 
-Please sign your commits, 
+Please sign off your commits, 
 to show that you agree to publish your changes under the current terms and licenses of the project.
 
 ```shell